Porous carbon materials have a variety of uses; for example they may be used: as electrodes for ultracapacitors, batteries, fuel cells and the like; as catalysts; as adsorbents; and as chemical reagents, among others. It is often necessary that the pore size of the carbon be controlled so as to optimize the properties of the material for particular applications.
A variety of techniques have been developed in the prior art for the preparation of porous carbon materials, and many of these methods involve the pyrolysis of a starting material. As is used herein, pyrolysis is understood to mean a chemical reaction brought about by heating which may comprise partial or complete degradation of a material wherein at least a portion of the material is converted to carbon. The prior art has developed a number of processes relying upon the use of different starting materials and different heating profiles to produce porous carbon materials via a pyrolysis reaction.
A number of approaches have been implemented in the prior art for the fabrication of porous carbon materials. In one approach, a starting mixture of carbonaceous materials such as natural or synthetic polymers, together with admixed metal particles such as Fe, Ni, and Co, is pyrolyzed. In the pyrolysis process, the metal particles activate the formation of mesopores. This method results in the production of a material which includes the metal particles. The presence of these particles is not always desirable, and removal of the particles is difficult. In other processes, carbonization of a precursor material takes place in the presence of a pore-forming template such as mesoporous silica. This process requires the use of highly corrosive acids such as hydrofluoric acid for the removal of the silica template. It has also been suggested in the prior art that various polymer blends can be pyrolyzed to produce porous carbons. However, such processes have heretofore been of limited utility since the geometry of the pore structure depends on the extent of reaction induced phase separation of the polymers, which is very difficult to control and predict.
As will be explained hereinbelow, the present invention is directed to simple to implement methods and materials for directly producing porous carbon via pyrolysis reactions. According to the methods of the present invention, the properties of the porous carbon may be selectably controlled by proper selection and control of the starting materials. Accordingly, the present invention may be employed to synthesize porous carbon materials having a very narrowly defined and precisely selected range of pore sizes.